Before any advice, I have questions. What is your climate? How rainy is it?
You would need to protect the cob additions from runoff from the yurt roof, as well as the added roofs, give enough overhang to route drips away from walls, and have foundation walls of stone high enough to keep splashes from hitting the base of the cob walls.
I think building under the gutter system or a wooden hallway would both work. If I were planning it I would probably go for the wooden hallway. Even though I've seen and even helped assemble a yurt before and know that the eaves of the yurt aren't super short, somehow that's how my mind remembers them. Either way, I think this is a cool idea.
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